The invention relates to a process for preparing hydrogenated or partially hydrogenated transition metal compounds having monocyclic, bicyclic or polycyclic ligands by hydrogenation of the corresponding unsaturated transition metal compound in a static mixer.
Transition metal compounds are gaining increasing importance as essential constituents of a new generation of catalyst systems for preparing polyolefins (xe2x80x9csingle site catalystsxe2x80x9d). These new catalysts consist, as is known from classical Ziegler-Natta catalysis, essentially of a transition metal compound as catalyst and an alkylaluminoxane as organoaluminium cocatalyst component. As transition metal compound, preference is given to using, for example, cyclopentadienyl, indenyl or fluorenyl derivatives of elements of group IVa of the Periodic Table of the Elements.
The transition metal compounds which can be used according to the invention have monocyclic, bicyclic or polycyclic ligands such as indenyl or fluorenyl, which may be substituted or unsubstituted. The transition metal compounds can be used as alkyl compounds, as halide compounds, as aryl or alkaryl compounds or as alkoxy compounds.
In contrast to conventional Ziegler-Natta catalysts, such systems have a high activity and productivity and are not only capable of controlling the product properties in a targeted manner as a function of the components used and the reaction conditions but also open up a route to hitherto unknown polymer structures having very promising properties with a view to industrial applications. The monocyclic, bicyclic or polycyclic transition metal compounds have a differing polymerization activity and selectivity depending on whether the polycycle is saturated or unsaturated. The hydrogenation and work-up of the transition metal compounds is sometimes technically complicated, the conversions are incomplete, the yields are often low and the products are correspondingly expensive.
Some possible ways of hydrogenating monocyclic, bicyclic or polycyclic transition metal compounds have been described in the literature (W. Kaminsky et al., Angew. Chem. 97 (1985), 507-508).
Some of these processes are technically complicated since they require, inter alia, low reaction temperatures at the beginning or multistage work-up processes and suffer from reduced yields as a result, or the hydrogenated transition metal derivative can often not be obtained in the purity necessary for a high catalyst activity.
It is therefore an object of the present invention to overcome these disadvantages of the prior art and to provide a simple and efficient process for the hydrogenation of monocyclic, bicyclic or polycyclic transition metal compounds.
The invention provides a process for preparing transition metal compounds having hydrogenated or partially hydrogenated monocyclic, bicyclic or polycyclic ligands, which is characterized in that the unsaturated monocyclic, bicyclic or polycyclic transition metal compound together with hydrogen is introduced continuously or all at once under pressure into a static mixer in the presence of a suitable solubilizer and a catalyst. The continuous introduction of hydrogen can also be carried out with return of unreacted hydrogen into the circuit.
Further embodiments of the invention are characterized by the claims.
According to the invention, preference is given to a preparative process in which hydrogen is introduced via a mixing nozzle into a solution or suspension of an unsaturated monocyclic, bicyclic or polycyclic transition metal compound in an aliphatic, cycloaliphatic or aromatic hydrocarbon, if desired a halogenated hydrocarbon, in a static mixer, preferably a flow tube with partial flow return (K. Hxc3xcbner, Chemie-Technik 6 (1987), 87-92). For the purposes of the present invention, the term solubilizer refers to diluents which lead either to a solution or to a suspension.